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| Ultimi arrivi - Mars Reconnaissance Orbiter (MRO) |
PSP_007151_1445_RED_abrowse-01.jpgColorful Layers in the Walls of an Unnamed Southern Crater (extra-detail mgnf - MULTISPECTRUM; credits: Lunexit)57 visiteThis extra-detail mgnf (enhanced to exaggerate color contrast) shows part of the North-facing walls of the crater, deeply carved by landslides. Rocky layers, mostly purplish in color, can be followed for hundreds of meters, poking through the loose materials that cover the slopes.
Locally, the rocky layers show patches of diverse colors (blue, green, yellow). These colors may be indicative of compositional differences in the rocky layers.MareKromiumMar 16, 2008
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PSP_007193_2640_RED_abrowse-01.jpgDefrosting Northern Dunes (extra-detail mgnf - MULTISPECTRUM; credits: Lunexit)57 visiteThis extra-detail mgnf shows a Region of the dunes that are just beginning to lose their seasonal ice cover. In most of the image the dunes are a muted red color. Where the sun is shining on the steep dune crests the frost is gone and dark dust is free to cascade down the sides. This thin layer of dust, like slope streaks found elsewhere on Mars, flows down around obstacles and may come to rest mid-slope.MareKromiumMar 16, 2008
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PSP_006991_1905.jpgSeeps (MULTISPECTRUM; credits: Lunexit)59 visitenessun commentoMareKromiumMar 07, 2008
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PSP_006991_1905_cut_b.jpgSeeps (MULTISPECTRUM; credits: Lunexit)74 visitenessun commentoMareKromiumMar 07, 2008
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PSP_007338_2640_RED_abrowse-1.jpgCaught in Action: Avalanches on North Polar Scarps (natural colors; credits: Lunexit)57 visitenessun commentoMareKromiumMar 07, 2008
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PSP_007338_2640_hires.jpgCaught in Action: Avalanches on North Polar Scarps (false colors; credits: NASA)55 visiteAmazingly, this image has captured at least four Martian avalanches, or debris falls, in action. It was taken on February 19, 2008, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.
The image to the left shows the context of where these avalanches occurred, with white boxes indicating the locations of the more detailed image portions shown to the right. All images are false color. Material, likely including fine-grained ice and dust and possibly including large blocks, has detached from a towering cliff and cascaded to the gentler slopes below. The occurrence of the avalanches is spectacularly revealed by the accompanying clouds of fine material that continue to settle out of the air. The largest cloud (upper images) traces the path of the debris as it fell down the slope, hit the lower slope, and continues downhill, forming a billowing cloud front. This cloud is about 180 meters (590 feet) across and extends about 190 meters (625 feet) from the base of the steep cliff. Shadows to the lower left of each cloud illustrate further that these are three dimensional features hanging in the air in front of the cliff face, and not markings on the ground. Sunlight is from the upper right.
Cameras orbiting Mars have taken thousands of images that have enabled scientists to put together pieces of Mars' geologic history. However, most of them reveal landscapes that haven't changed much in millions of years. Some images taken at different times of year do show seasonal changes from one image to the next, however, it is extremely rare to catch such a dramatic event in action. (Another, unrelated, active process that has been captured by Mars cameras are dust devils.) Observing currently active processes is often a useful tool in unlocking puzzles of the past for scientists studying the Earth. Working from primarily still images, it is harder for scientists studying Mars to rely on this tool. The HiRISE image of avalanching debris is a very rare opportunity to directly do so.
The scarp in this image is on the edge of the dome of layered deposits centered on Mars' north pole. From top to bottom this impressive cliff is over 700 meters (2300 feet) tall and reaches slopes over 60 degrees. The top part of the scarp, to the left of the images, is still covered with bright (white) carbon dioxide frost which is disappearing from the polar regions as spring progresses. The upper mid-toned (pinkish-brownish) section is composed of layers (difficult to see here) that are mostly ice with varying amounts of dust. The darkest deposits below form more gentle slopes, less than 20 degrees, and are mainly composed of two materials: mid-toned layers, possibly ice-rich, that form small shelves, and more mobile, wide-spread, sand-sized dark material. The wavy forms on the flatter areas to the right are dunes.
The upper, steepest section, which appears highly fractured due to blocks pulling away from the wall, is the likely source zone for the falls. The precise trigger mechanism is not yet known, although the disappearance of the carbon dioxide frost, the expansion and contraction of the ice in response to temperature differences, a nearby Mars-quake or meteorite impact, and vibrations caused by the first fall in the area, are all possible contributors.
By comparing images taken before the fall (such as HiRISE image PSP_007140_2640) and after the fall, we may be able to see where material has disappeared from the steep scarp and where it has appeared on the gentler slopes below, possibly as larger blocks, diffuse streaks, or other debris deposits. By imaging this scarp throughout the polar summer, we may be able to determine how much material falls over a given time period. These observations would help determine how much, and at what rate, ice is being eroded from the cliff. Understanding the processes and rates of erosion will help determine how the polar landscape has evolved, and help reveal how volatiles, such as water and carbon dioxide ices and gases, move around Mars.
The precise composition of the ice-dust mixture making up layers in the upper, steepest section of scarp is not known. However, detailed measurements of the volume of material removed, the configuration of the source area, and the steepness of the slope can be used to estimate physical properties of the material that may relate to composition.
The complete image, HiRISE PSP_007338_2640, is centered at 83.7 degrees latitude, 235.8 degrees east longitude. The image was taken at a local Mars time of 1:05 PM and the scene is illuminated from the west with a solar incidence angle of 70 degrees, thus the sun was about 20 degrees above the horizon. At a solar longitude of 34.0 degrees, the season on Mars is northern spring.
NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace and Technology Corp., Boulder, Colo.
MareKromiumMar 05, 2008
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PSP_006969_1725_RED_abrowse-01.jpgThe Floor of Noctis Labyrinthus (extra-detail mgnf - MULTISPECTRUM; credits: Lunexit)55 visiteThe most striking feature of many of these knobs is a thin, bright band which often wraps around the edges near the bottom, as in this extra-detail mgnf. This image was acquired in order to investigate whether this is an exposed layer of rock or the shoreline of a former body of water.
HiRISE resolves details of the bright band that indicate that this is an unusual layer of rock, rather than an old shoreline. In several places, the band is broken up along cracks, sometimes forming boulders. This indicates that the band is solid rock, while material left on a shoreline should be loose sediments. It is now exposed as rings and arcs where erosion has cut deeply enough to expose the layer.
This band must indicate some unusual event in the geologic history of the region when a different type of rock was deposited; it is strikingly different in color from the other rocks. Although it is not a shoreline, it could be material that was deposited on the floor of a much older lake or sea and then buried by other rock; it could also have been laid down by other sedimentary processes or as volcanic ash.
MareKromiumMar 05, 2008
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PSP_007043_2650-BLUE-MarsPolarDunes2_hirise_big-00.jpgSand Dunes Thawing on Mars (False Colors; credits: NASA)64 visiteCaption NASA:"What are these strange shapes on Mars? Defrosting sand dunes.
As spring now dawns on the Northern Hemisphere of Mars, dunes of sand near the pole, as pictured above, are beginning to thaw.
The Carbon Dioxide and water ice actually sublime in the thin atmosphere directly to gas. Thinner regions of ice typically defrost first revealing sand whose darkness soaks in sunlight and accelerates the thaw. The process might even involve sandy jets exploding through the thinning ice. By Summer, spots will expand to encompass the entire dunes. The Martian North Pole is ringed by many similar fields of barchan sand dunes, whose strange, smooth arcs are shaped by persistent Martian Winds".MareKromiumMar 03, 2008
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PSP_007043_2650-BLUE-MarsPolarDunes2_hirise_big-01.jpgSand Dunes Thawing on Mars (Natural Colors; credits: Lunexit)55 visitenessun commentoMareKromiumMar 03, 2008
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PSP_006952_1870_RED_abrowse-01.jpgDunefield in West Arabia Terra Unnamed Crater (extra-detail mgnf - RAW Frame; credits: NASA/JPL/Univ. of Arizona)56 visiteBarchan dunes are commonly found on Earth, and are generally crescent-shaped with a steep slip face bordered by horns oriented in the downwind direction (see here).
Barchan dunes form by unidirectional winds and are good indicators of the dominant wind direction. In this case, the strongest winds blew approximately North to South.
These dunes are most likely composed of basaltic sand that has collected on the bottom of the crater. Superimposed on their surface are smaller secondary dunes which are commonly seen on terrestrial dunes of this size.
Many smaller and brighter bed forms — most likely small dunes or granule ripples — also cover the substrate between the larger dark dunes.
The dark dunes overlie the small bright bed forms indicating that the darker dunes formed more recently.MareKromiumFeb 22, 2008
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PSP_006891_1970_RED_abrowse-01.jpgAt the base of the Olympus... (EDM - Saturated Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)56 visiteThe bottom right part of the cutout has a much flatter and smoother surface. These are younger lava flows that have buried the lower part of the volcano. When lava flows form vast smooth sheets, they are called "flood" lavas.
In the bottom of the cutout, the flood lavas have odd, wiggly looking plateaus. These are parts of the lava crust that were lifted up when more liquid lava was injected into the middle of the slowly solidifying lava flow.
This process is called "inflation" and is seen on many lava flows on Earth. These younger lava flows are cut by two different sets of faults. One makes the branching valley in the flood lavas and the other creates the sinuous ridge and valley along the edge of the Olympus Mons lava flows.
Lower resolution images that cover a broader area suggest that the sinuous fault is an old buried structure that has been more recently reactivated.MareKromiumFeb 22, 2008
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PSP-P14_006600_1881_XI_08N102W_071223sub_large.jpgUnusually-shaped Landform in Tharsis (MULTISPECTRUM; credits: Lunexit)77 visiteThis picture of a Landform (...) was acquired nearly two months ago by the CTX on 23 December 2007.
The Landform is about 1 Km (0,62 miles) across. The feature is located among lava flows South-East of the giant Tharsis volcano, Ascraeus Mons.
This picture is a sub-frame of CTX image P14_006600_1881_XI_08N102W_071223 and is located near 8,3° North Lat. and 101,9° West Long.MareKromiumFeb 19, 2008
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